Piezo transducer controller and method having adaptively-tuned linear damping

1. A distance measurement method that comprises: adjusting, in a linear damping module, at least one of: a shunt resistance value and a shunt reactance value; driving a piezoelectric transducer to transmit ultrasonic pulses; enabling the linear damping module to damp reverberation after each transmitted ultrasonic pulse; measuring reverberation periods when the linear damping module is enabled; associating trends in the reverberation periods with adjustments to said values; repeating adjustments associated with reverberation period reductions and reversing adjustments associated with reverberation period increases.

2. The method of claim 1 , further comprising disabling the linear damping module after damping is finished and detecting echoes of transmitted ultrasonic pulses.

3. The method of claim 1 , wherein said adjusting is performed on only one of the shunt resistance and shunt reactance before a given enabling of the linear damping module.

4. The method of claim 1 , further comprising characterizing the piezoelectric transducer and performing a coarse tuning of the shunt resistance and shunt reactance before performing said driving, enabling, measuring, associating, and repeating operations.

5. The method of claim 4 , wherein the characterizing includes measuring a parallel capacitance C P of the piezoelectric transducer.

6. The method of claim 5 , wherein said measuring the parallel capacitance of the piezoelectric transducer includes measuring a time required for a current source to charge the transducer to a reference voltage.

7. The method of claim 5 , wherein said measuring the parallel capacitance of the piezoelectric transducer includes temporarily scaling the shunt inductance up and measuring a reverberation frequency f P .

8. The method of claim 5 , wherein said measuring the parallel capacitance of the piezoelectric transducer includes measuring a rate of change in a phase difference between a current in the shunt reactance and a piezoelectric transducer voltage.

9. The method of claim 5 , wherein said characterizing further includes measuring a series resonant frequency f S , and wherein said coarse tuning includes setting the shunt reactance to an inductance value expressible as L P = 1 ( 2 ⁢ π ⁢ ⁢ f S ) 2 ⁢ C P .

10. The method of claim 4 , wherein said characterizing includes measuring a decay rate α to estimate a series inductance L S of the piezoelectric transducer, and said coarse tuning includes setting the shunt resistance value based at least partly on the estimated series inductance L S .

11. The method of claim 10 , wherein the estimated series inductance L S is expressible as L S = R S 2 ⁢ α , R S being a series resistance of the transducer estimated as a ratio of a peak driving voltage for the transducer to a peak short-circuit current of the transducer.

12. The method of claim 10 , wherein the shunt reactance is a tunable inductance having a value L P , and said coarse tuning includes setting the shunt resistance to a value expressible as R D =πf S √{square root over (L S L P )}, f S being a measured frequency of said reverberation.

13. A piezoelectric transducer controller that comprises: a transmitter that drives a piezoelectric transducer to transmit ultrasonic pulses; a linear damping module having a shunt resistance and a shunt reactance to damp reverberation after each transmitted ultrasonic pulse; a reverberation timer that measures reverberation periods when the linear damping module is enabled; at least one updater unit that adjusts a value of at least one of: the shunt resistance and the shunt reactance; and an allocator unit that associates trends in the reverberation periods with adjustments to said value, the at least one updater unit repeating adjustments associated with reverberation period reductions and reversing adjustments associated with reverberation period increases.

14. The controller of claim 13 , further comprising core logic that disables the linear damping module after damping is finished and detects echoes of transmitted ultrasonic pulses.

15. The controller of claim 13 , wherein said at least one updater unit adjusts only one of the shunt resistance and shunt reactance before a given use of the linear damping module to damp reverberation.

16. The controller of claim 13 , further comprising core logic that characterizes the piezoelectric transducer and performs a coarse tuning of the shunt resistance and shunt reactance before coordinating said driving, enabling, measuring, associating, and repeating operations.

17. An ultrasonic sensor that comprises: a piezoelectric transducer; a transducer controller coupled to the piezoelectric transducer to perform a distance measurement method that includes: adjusting, in a linear damping module, at least one of: a shunt resistance value and a shunt reactance value; driving the piezoelectric transducer to transmit ultrasonic pulses; enabling the linear damping module to damp reverberation after each transmitted ultrasonic pulse; measuring reverberation periods when the linear damping module is enabled; associating trends in the reverberation periods with adjustments to said values; repeating adjustments associated with reverberation period reductions and reversing adjustments associated with reverberation period increases.

18. The sensor of claim 17 , wherein the method further includes: disabling the linear damping module after damping is finished and detecting echoes of transmitted ultrasonic pulses.

19. The sensor of claim 17 , wherein said adjusting is performed on only one of the shunt resistance and shunt reactance before a given enabling of the linear damping module.

20. The sensor of claim 17 , wherein the method further comprises characterizing the piezoelectric transducer and performing a coarse tuning of the shunt resistance and shunt reactance before performing said driving, enabling, measuring, associating, and repeating operations.